In recent years, silicon carbide has been increasingly employed as a material for a semiconductor device such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) in order to allow a higher breakdown voltage, lower loss and the use in a high-temperature environment and the like of the semiconductor device. Silicon carbide is a wide band gap semiconductor having a band gap wider than that of silicon which has been conventionally and widely used as a material for a semiconductor device. By employing the silicon carbide as a material for a semiconductor device, therefore, a higher breakdown voltage, lower on-resistance and the like of the semiconductor device can be achieved. A semiconductor device made of silicon carbide also has the advantage of exhibiting less performance degradation when used in a high-temperature environment than a semiconductor device made of silicon.
In a MOSFET, a gate runner made of a material having lower electrical resistivity than that of a gate electrode may be formed on the outer periphery for efficient transmission of a gate signal to the gate electrode. According to a MOSFET described in Japanese Patent Laying-Open No. 11-266014 (PTD 1), for example, a gate electrode (gate runner) is arranged in an outer peripheral region on a silicon carbide substrate. According to a MOSFET described in WO 2010/098294 (PTD 2), a gate electrode is arranged above a p type semiconductor layer, and a pad portion for the gate electrode (gate runner) is arranged in contact with the gate electrode.
According to the MOSFETs described in the aforementioned documents, an oxide film is formed between the pad portion for the gate electrode (gate runner) and the silicon carbide substrate in order to ensure insulation performance between the pad portion for the gate electrode and the silicon carbide substrate.